1. Field of the Invention
This invention relates to a two part curable latex-reinforced polyurethane sealing composition useful for sealing structures, such as sewer lines, to minimize or prevent water leakage through voids, joints, cracks, fissures or other openings therein. In another aspect, it relates to a method for sealing such structures with said sealing composition. In yet another aspect it relates to the structure so sealed.
2. Background of the Prior Art
There is a host of water-bearing or holding structures disposed above or beneath ground level, such as sewer lines, aqueducts, tunnels, wells, settling ponds, and basements of buildings, made of materials such as siliceous materials (e.g., concrete, brick and mortar), plastics (e.g., polyvinylchloride), cast iron, or wood (e.g., cypress or cedar). Because of the nature of such construction material or the manner of constructing such structures or their locations, such structures inherently have, or develop with time, various discontinuities such as openings, cracks, fissures, joints, or the like which provide an entry or pathway for the undesirable ingress or egress of water into or from such structures. Even hairline cracks or pin-hole size openings in an otherwise sound or water-impervious structure can result in a damaging and costly leakage from a temporary or permanent water source.
For example, sewer lines made of concrete (a brittle and unyielding construction material) normally experience the incursion or leakage of ground water via the interfaces defined by the abutting components or members of the structure, or via joints, holes, cracks, or fissures in the structure. Such leakage is generally tolerable in sewers up to a certain point without affecting the usefulness and serviceability of the structure. However, when a heavy rainfall occurs, a large amount of surface or run-off water penetrates the soil and accumulates in excavations surrounding the sewer line, raising the exterior hydrostatic head of the water, until the water leakage or incursion into the structure increases to an undesirable and even intolerable level. Since water has a propensity to find the path or drainage area of least resistance, the incursion of water into the sewer system may reach such high levels that the capacity of the downstream sewage treatment reservoir or pond is exceeded and untreated or insufficiently treated sewage is discharged to rivers or lakes causing pollution thereof. The water resulting from such incursion may also cause the flooding of basements of buildings.
Water-holding structures, such as concrete irrigation water courses or aqueducts or dikes, bearing a static head or flowing stream of water, also experience leakage due to holes, cracks, fissures, and the like, such leakage being an uneconomical loss of water as well as hazardous in many circumstances.
A host of sealing compositions and sealing techniques have been used to prevent the ingress or egress of water into or from such structures. Some sealing materials, such as mortar, shrink upon setting and curing to create cracks or fissures. Some sealants which are pumped into soil surrounding the structure to be sealed are limited to fine grain sand or soil. Other sealing materials must be placed in a dry environment or used in a dry, powdered form and they, consequently, lack mobility and cannot be extensively dispersed or placed in large leakage or drainage areas. Some sealing compositions require heat, or contain water-immiscible hydrocarbon solvents, and thus, their application is costly and generally limited to dry, clean environments. Other multi-component systems require careful metering and mixing or have a limited pot life. The application equipment for many of the prior art sealing techniques is cumbersome and costly and many of these techniques are limited only to areas which are readily accessible, easily dried, and suitable for cleaning.
Curable polyurethane compositions comprising isocyanate-terminated prepolymers based on polyols, have been disclosed as sewer grouting compositions and sealing agents for sewers and similar uses (see U.S. Pat. No. 3,985,688, Canadian Pat. No. 1,035,521 and British Pat. Specification No. 1,486,232). Also known is the use of curable isocyanate prepolymers with water to consolidate soil (see U.S. Pat. No. 3,719,050). These prior isocyanate-terminated prepolymer compositions frequently have limited utility, however, because of one or more reasons. Some may cure to form a cured tough, highly cohesive mass making it difficult to remove contacting equipment after curing. Others may produce relatively compressible cured compositions or foams which do not have sufficient compressive strength to withstand the pressures encountered in use conditions, e.g., when used to seal a sewer. Others may undergo dramatic volume fluctuations with changing environmental conditions, such as changes in moisture conditions. Such volume changes make it difficult to maintain an adequate seal of a leaking sewer line.
Perhaps the most successful commercially acceptable composition employed as a sewer sealing composition is that based upon acrylamide which is used typically as a liquid which is pumped with specially designed equipment into the site of the leak and into the surrounding soil to form a cured gel which inhibits or prevents leaking. In fact, much of the sewer sealing equipment employed in the United States and in other countries has been designed to utilize acrylamide type sealing compositions. Such compositions are desired, not only for their ability to appropriately seal leaks in sewers and in other areas, but also because of their compatible viscosity range which is easily adjustable, providing an easily pumpable mixture, their desirable cure rate and their physical properties achieved upon curing.
The cured acrylamide material generally has an acceptable compressive strength capable of withstanding the compressive forces encountered in sealing situations such as in sewers and an acceptable resistance to shrinking which is required for the cured material to function properly as a sealant as hydrological conditions vary at the sealing site. Additionally, the acrylamide type sealing compositions will cure in a reasonably brief period of time without requiring prolonged delays so that equipment may be advanced to new sealing locations. This is important when sealing sewer lines, for example, where a sewer packer is employed utilizing an inflatable sleeve which is required to be inflated within the sewer line being sealed until the curing of the sealant has been accomplished.
Additionally, acrylamide-type sealing compositions will cure to a somewhat weakly cohesive mass which permits easy removal of the contacting sealing equipment, e.g., the sewer packer, so that it may be moved to a new location without difficulty.
While the acrylamide-type sealing compositions have all these desirable properties and have proven to be extremely valuable in such applications, they have several serious defects including a serious toxicological problem which may lead to its being banned for sealing sewers in the United States and in other concerned countries. This situation requires the replacement of the acrylamide-type sealants with a suitable substitute.
While many sealing compositions are known, it is highly desirable to replace the acrylamide-type sealing compositions with one having the same or similar physical properties, both in the liquid state and in the cured state, without the adverse toxicological problems. The present invention not only accomplished this result, but it provides a sewer sealing composition which is better than the acrylamide-type sealants.